Conventionally ultra-pure water is used for diluting chemicals (for instance for diluting 98% sulfuric acid to a desired density) or for preparing chemicals (for instance dissolving sodium hydroxide to prepare a 1 N sodium hydroxide sodium), for washing vessels such as a beaker or a tank, or for removing a chemical solution or residue of a chemical solution from a surface of a silicon wafer steeped into a chemical solution. Also ultra pure water is used as a raw material for obtaining hydrogen or oxygen by means of electroanalysis. Thus, a range of use of ultra pure water is rather narrow.
On the other hand, modification of characteristics of a surface material formed on a metallic material (such as control of the composition of the surface material) is executed by controlling a gas element or a reaction temperature when the surface material is formed, or making the surface react with other gas after the surface material is formed.
FIG. 13 shows an XPS analysis diagram for a surface material in a case where composition control is executed by changing the gas after a reaction for generation of the surface material. FIG. 13A is an XPS analysis diagram for a case where SUS 316L is reacted to fluorine gas for 8 minutes under a temperature of 220.degree. C., and FIG. 13B shows a case where a thermal processing is executed, after the processing in FIG. 13A, for 24 hours in a nitrogen atmosphere under a temperature of 400.degree. C. In case of the surface shown in FIG. 13A, a ratio of Fe vs F is 1:2.27 indicating a non-stoichiometric structure, while the surface shown in FIG. 13B has an Fe Vs F ratio of 1:2.00 indicating a stoichiometric structure of FeF.sub.2.
FIG. 14 shows a result of comparison between a compound having a stoichiometric structure and that having a non-stoichlometric structure by exposing them to a fluorine gas and checking the barrier effect to the fluorine gas in terms of consumption pressure of a fluorine gas. As clearly shown in FIG. 14, in case of a surface having astoichiometric structure as indicated by the white circle, a pressure of fluorine is constant, and consumption of fluorine gas is not observed, however, in case of a non-stoichiometric structure as indicated by the black circle, a pressure of fluorine gas decreases in association of elapse of time, which indicates consumption of fluorine gas. Namely a surface not having a stoichiometric structure dose not have a barrier effect against a fluorine gas. Thus a surface having a stoichiometric structure is stable. However, in the conventional method, a long time processing under a high temperature is required.
It is an object of the present invention to provide a method of modifying a surface material and an apparatus for the same enabling easy modification of characteristics of a surface material (control of chemical composition of a surface material) and new application of ultra pure water.